This invention relates generally to a novel method and apparatus for supporting electric heating elements in a furnace insulated with ceramic fiber.
More particularly, this invention concerns a method and apparatus for utilizing a ceramic fiber insulation module of a unique design which is operable to support electric resistence heating coils with a minimum likelihood of short circuit or heat loss.
Electric industrial furnaces or ovens, particularly those used for annealing, include resistance heating elements. These elements are metallic ribbons or wires which have been formed into a serpentine or sinusoidal configuration and are ordinarily supported on hangers which are attached to the furnace wall or casing.
There are a wide variety of known techniques for constructing and insulating industrial furnaces utilizing electric heating elements. For example, a furnace may be constructed from steel and insulated either internally or externally with ceramic material. Some furnaces are constructed of fire brick or have a fire brick lining inside a steel casing. In any event, to achieve satisfactory thermal efficiency, industrial furnaces will generally be provided with insulation of one form or another.
The resistence elements used in electric furnaces have a relatively short useful life as a result of failure or burnout. A failure or burnout may be occasioned by localized heating, short circuits, thermal stress in the heating elements, defects in the manufacture of the heating elements, or a variety of other known reasons. Therefore, these heating elements need to be replaced or repaired from time to time. When replacement or repair is required, it is necessary to cool the furnace to enable personnel to effect the necessary repairs. The shutting down of a furnace results in expensive down-time for the operator of the furnace, and additionally, results in an enormous waste of fuel and energy.
In the past, it has been common to insulate high temperature furnaces and the like with ceramic fiber insulation modules. These modules may take a variety of forms. For example, there is available an insulation module comprised of resilient fiber insulation arranged with the fibers or planes of the fibers lying in planes generally perpendicular to the major surfaces of the module. Other modules are fashioned from ceramic fiber insulation blanket which has been folded into an accordian or serpentine arrangement and then compressed slightly. Yet other modules are available which are comprised of vacuum-formed ceramic fiber and which are relatively rigid in construction. In addition, ceramic fiber insulation blanket may be used without benefit of folding or rearrangement and the like to provide satisfactory insulation characteristics. In any event, the term "module" is intended to encompass all of these as well as other types of furnace insulation materials.
When insulation modules of the ceramic fiber type are utilized to insulate a furnace, these modules are ordinarily impaled on studs which are welded or otherwise attached to the furnace casing or wall. These studs serve both to maintain the insulation module in position and to provide an anchoring arrangement to support electric resistence heating elements. Other arrangements are known whereby an anchor for a heating element is embedded in fire brick used to construct or insulate the interior of a furnace. When the interior of the furnace is lined with fire brick, and metallic anchors have been secured to the fire brick, an electric heating coil is affixed to these anchors.
Other known arrangements utilize ceramic panels which are positioned within a furnace in a manner overlying the interior insulation. Electric heating elements then are attached to the panel.
Many of the above problems are compounded in instances where it is desirable to replace only the insulation material in a furnace. That is, many known methods and apparatus for supporting electric heating elements are incompatible with any known arrangements for repairing or replacing insulation material. These known heating element support arrangements require an extensive and cumbersome dismantling in order to facilitate replacement of insulation.
In instances where it is desirable to construct a ceramic fiber veneer over the existing fire brick in a furnace, the construction of an entirely new system for supporting electric heating coils may be required. Because of the great expense in reconstructing a heating coil system, some furnace operators may be discouraged from repairing or replacing the insulation in their furnaces with the result that some furnaces may be operated at highly inefficient levels.
The problems ennumerated in the foregoing are not intended to be exhaustive, but rather are among many which tend to impair the effectiveness of previously known systems for supporting electric heating coils in a furnace. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that those arrangements for supporting heating coils in a furnace known in the art have not been altogether satisfactory. Whereas prior art arrangements have exhibited at least a degree of utility in supporting electric resistence heating elements in a furnace, room for significant improvement remains.